A solenoid valve is an electromechanical valve that operates by controlling an electric current that flows through a solenoid. While solenoid valves exist in many different configurations, one particular configuration includes a movable metallic plunger and a co-axially mounted stationary metallic core. One end of the plunger can contact a guide spring. A valve seat can be attached to the plunger with the guide spring in between. Alternatively, the guide spring can act as a valve seat. The other end of the plunger can contact the stationary metallic core or be coupled to the core using a biasing member such as a spring. The biasing member can bias the plunger assembly against the orifice creating a normally closed valve. It is also known in the art to bias the plunger up towards the stationary metallic core, creating a normally open valve.
When a current flows through a coil that surrounds the stationary metallic core a magnetic flux is created. In one particular design of a solenoid valve, the metallic core partially surrounds the plunger and thus, when a current flows through the coil the magnetic flux created pulls up on the plunger.
One problem that has limited the operation of solenoid valves of this design is the limitation on the pressure rating. Typically, the highest area of stress is the internal pressurization in the portion of the magnetic core wall that encases the plunger. For example, in solenoid valves rated to about 1500 psi with internal diameters of approximately ⅜″, the valve requires the wall to have a thickness of about 0.017″. The wall thickness is designed to be as thin as possible, while still operating safely, in order to reduce the magnetic flux diverted away from the plunger. The thinner that the wall can be designed, the higher the magnetic reluctance of the path through the wall and thus, the smaller the amount of magnetic flux lost. Magnetic flux lost to the core wall reduces the pulling force on the plunger. Therefore, it is desired to keep the amount of magnetic flux lost to the core wall to a minimum.
In the prior art, in order to increase the pressure rating of the solenoid valve, the wall thickness of the core was increased. For example, to achieve a 4500 psi rating, the prior art wall could be increased to approximately 0.055″ for the same internal diameter and wall material. This increase in wall thickness reduced the magnetic reluctance of the wall and consequently, a significant portion of the flux flowed through the wall, thereby decreasing the pull on the plunger. While this was an undesired side-effect, the prior art wall thickness was required to be increased in order to satisfy higher pressure ratings.
The present invention overcomes this and other problems and an advance in the art is achieved.